Biomass

BasicsEnergy from the sun, via photosynthesis in plants

This is the same energy we use as food

This is the same energy that made fossil fuels; fossilfuels are concentrated over time by the heat andpressure within the Earth.

The oldest form of energy used by humans: wood fire.

Efficiency

Plants use only a tiny amount of the sun’s energy forphotosynthesis, less than 1%.

The efficiency of photosynthesis is low, about 5%maximum (solar energy to energy in sugar).

•Corn field: about 1 to 2% efficient•Pine forest: less than 1% efficient

Efficiency of burning biomass to electricity is about thesame as with fossil fuels

Potential

Potential is impressive

United States:•If we harvest all crops for energy on all land currentlyunder cultivation in the United States, the amount ofenergy available at 100% conversion efficiency isabout equal to the total annual energy used in theUnited States.•At more realistic conversions, biomass maximum isabout 30% at today’s use rate

Potential

The worldThe amount of energy in the global biomass is about 8times more than the amount of energy currently usedglobally.

These are maximum estimates:•We need biomass for food as well•We cannot (should not?) cultivate all land surfaces•Burning efficiency needs to be considered

What is biomass?Chemically:

Plant material is a combination of cellulose (about60%), lignin (about 30%), and other organic materials(about 10%).

Cellulose is the structural material in plants (fibers)

Lignin is the glue that holds the cellulose together

Both start with simple sugars (glucose) made inphotosynthesis

What is biomass?Physically:

Any plant tissue can be used for energy, but the faster the plantgrows, the more useful it is.

Growing energy crops.

Poplar trees grown for energy.These are 2 year old seedlings.Genetically engineered andbred for fast growth.

What isbiomass?

Trees: poplarand willowcan be grownto large sizevery rapidly: 7year oldpoplars inpicture.

Harvesting trees is done usingstandard forestry equipment.

GrassesSwitchgrasscan be grownrapidly (oneseason), andharvestedusing standardfarmimplements.

Grasses

Grasses areattractive alsobecause theycan be grownin climatesunfavorable totrees.

The overall area of land in the US suitable forenergy crops:

Growing plants

This illustrates that plants need more thansunlight to grow. They need sunlight and

Carbon dioxideWaterMacronutrients (nitrogen andphosphorous)Micronutrients (for example, iron)

Growing plants

Keep in mind that faster growing plants needmore of all of these. You don’t get somethingfor nothing!

Poplar and switchgrass, for example, needintensive fertilizing and plenty of water toachieve the high growth rates

Pros•Relatively lowpollution.

•Carbon dioxidereleased isconverted back toplants (carbondioxide neutral)

Pros•Multiple uses ofbiomass.

•Bioproducts includeplastics, medicinesand other materialstraditionally producedfrom oil.

Pros•Reduce waste, and save landfill space.

About 85% of material put into landfills is plant material thatcould be combusted for energy. Paper alone is about 55%.

Key is waste separation. It is expensive to separate paperfrom paint, for example; and burning paper contaminatedwith paint creates toxic wastes that get into the atmosphere.

About 15% of waste is currently burned, (for energy or, inmost cases, for waste reduction).

Pros

•Relatively cheap.

Costs today are about 9 cents per kilowatt hour. This isabout the same, or less, as energy from fossil fuels.

Costs are expected to be even less in the future ascrops grown for fuel become more available.

How does it work?

How do we convert biomass energy to usefulforms of energy?

•Direct burning•Gasification•Cofiring•Fermentation

Direct burningDirect burning is as it sounds. Plant material is chipped, dried,and then burned to boil water, make steam, and thenelectricity.This is a relatively inefficient technology and the mostpolluting method of energy from biomass.

Gasification

Gasification is the conversion of biomass into a gasand carbon powder.

Process begins with pyrolysis. Biomass is combinedwith hot sand (800˚C). This reduces biomass to gasesand carbon powder.

The gases are used to run a turbine. They are thenrecycled back to be burned for fuel. Increases overallefficiency

GasificationAdvantages are:•Cleaner (butstill ash to dealwith)•More efficient,40%demonstrated,50% possible

CofiringCofiring is the use of biomass in combination withcoal.

Advantages are:•Biomass cheaper than coal, so cofiring is cheaperthan burning coal alone•Less sulfur oxides (less coal burned); pollution andcost savings•Easy to adapt current systems to cofiring

FermentationFermentation is the production of alcohol (ethanolmainly) from sugars in biomass. The alcohol can beburned alone, or mixed with gasoline.

•Mixtures can range from 10% ethanol (often usedto reduce pollution) to 100% ethanol•Ethanol is more expensive than gasoline currently(although comparisons are hard to make due to themany subsidies for both).•Net energy yield from ethanol is low, could bemuch better with cellulosic ethanol

FermentationEnergy from ethanol is less than that from gasoline.But it produces less pollution (especially carbonmonoxide) as it burns at a higher temperature, andthus more fully oxidizes.

Most ethanol is from corn (about 95%). The rest isfrom sugarcane. Brazil uses ethanol from sugarcane topower about 1/3 of its cars.

Keep in mind that energy is needed to produce ethanol, and thatthis energy currently comes form fossil fuels.

Conversionto methane

Conversion to methane

Methane production is most useful withanimal and human wastes, as well aslandfill wastes, where it happens naturally.This is attractive in rural areas, and canhelp reduce ethanol costs by supplyingenergy needed in the corn to ethanolprocess.

Potential

Currently we get less than much less than 1% of our energy inindustrialized countries from biomass. This could be as high as10%, mostly gasification or cofiring.

Ethanol could be more useful if cellulosic ethanol works. Thiswill add to biomass potential. But ethanol is unlikely to directlyreplace gasoline. (We will probably see a combination oftechnologies used to replace gasoline…)

Developing countries already use biomass, but in a subsistencelifestyle. Biomass in developing countries is non-renewable.

Potential

Future of biomass energy depends strongly on land,water and nutrients available.

This means:•This source of energy must compete with foodproduction.•This energy source will have less dependabilityyear to year as climate will affect crop yields.